1. Field of the Invention
This invention relates to the carbothermic production of metals, such as aluminum and silicon, which employ carbonaceous reducing agents under thermal reduction conditions.
2. Description of Prior Art
Silicon metal has been produced commercially for many years by the thermal reaction of carbon with oxides of silicon to produce silicon metal and carbon monoxide. The carbon monoxide, is then further oxidized by contact with air and emitted to the atmosphere as carbon dioxide.
Ferroalloys, iron and steel are also produced by the thermal reaction of carbonaceous reductants with oxides of the metals to be produced, emitting carbon oxide gases to the atmosphere.
Aluminum metal has been and is presently being produced commercially by the electrolysis of a fluoride bearing molten salt. This process also emits carbon dioxide to the atmosphere.
Public concern is increasing over the environmental effects of carbon dioxide emissions to the atmosphere, and especially over the emissions of fluorocarbon gases. It is therefore understandable that interest is increasing in finding processes for producing metals which do not emit carbon oxide gases to the atmosphere, and especially for finding a process for producing aluminum which does not emit carbon dioxide, and one which does not use fluoride bearing materials.
Electrolysis processes for the production of aluminum are being investigated in a cooperative effort of industry and the U.S. Department of Energy. These processes employ inert anodes and, in principle, could emit oxygen instead of carbon dioxide. However the processes presently being studied still employ fluoride bearing electrolytes.
An electrolysis process for producing aluminum employing a chloride electrolyte has been proposed. However this process would emit carbon dioxide, and, because of reported problems with various chlorine based compounds as by-products, the work on this process has not resulted in significant production of aluminum.
Production of aluminum by carbothermic reduction can be performed without the involvement of fluorine or chlorine based compounds, except for the use of chlorine based gases as are currently used in remelting aluminum and preparing it for commercial use. Carbothermic production of aluminum therefore offers an important relief from the problem of fluorocarbon gas emissions from aluminum production facilities. However, carbothermic production of aluminum produces approximately twice the carbon dioxide per pound of aluminum produced as the currently used electrolytic process produces. Consideration of this fact has had the effect of retarding progress toward the proof of a commercial process which would eliminate the fluorocarbon emission problem in the production of aluminum.